Ex coming back

I(20m) have been with my new girlfriend(19f) for coming two months now. I broke up with my ex in December, and the break up was grueling. I missed her, wanted her back more than anything. I went to therapy, moved on with multiple other women as best as I could. I met a new girl(my current girlfriend) and have enjoyed her immensely ever since. She’s the woman I think about constantly from the moment I wake up, to when I go to sleep. We hangout constantly, even with the long distance situation we’re currently having, and she even told me today for the first time ever, “I love you”. We click very well, and seriously enjoy one another. Her family is amazing, she’s amazing. However, I, from time to time, do miss my ex, and do wish I still could get her back. Fast forward to the present, I found out my ex was stalking me. She would unblock me from time to time, and always check my story. Just recently, she slipped up and liked it, and immediately blocked me. My dilemma is that I miss my ex, and I do love having my current girlfriend, and I also want to know why my ex is stalking me, does she miss me too? Am I a monster for having these feelings? Please, someone steer me on the right track.